What is wall putty (skim coat) and what does it do?
Wall putty (skim coat) is a blend of cement, mineral fillers and polymer additives used to smooth and level walls before painting. A good skim coat hides render imperfections, improves paint adhesion and reduces paint consumption, giving an even, smooth final coat. The BuMaSKIM range covers both interior and exterior walls.
How do interior and exterior putties differ?
Exterior putty (BuMaSKIM PES, EW, EG) contains higher polymer and cement content to withstand sun and rain, resist water and cracking, and hold adhesion under thermal movement; interior putty (BuMaSKIM PIS, IW, IG) is optimised for fineness and easy sanding to achieve a beautiful finish. Using interior putty outdoors leads to early peeling and chalking.
Is skim coating required before painting?
It is not mandatory, but strongly recommended where a high-quality finish matters: skim coating gives a flat, smooth surface, an even paint film and saves 15–20% of topcoat paint. Without it, the render must be finely floated and a defect-hiding primer used. For exterior walls, prefer a waterproof skim coat such as FinishSKIM for added rain protection.
What are the steps of a proper skim coating process?
Step 1: verify the render is dry enough (usually 7–14 days, moisture below 16%) and clean off dust and grease. Step 2: mix the powder with water at the correct ratio, let it slake a few minutes, then remix. Step 3: apply a thin, even first coat, let it dry, then a second coat, keeping total thickness under 3mm. Step 4: after drying, sand with fine paper, dust off, then prime — avoid over-sanding, which destroys the key for paint.
How many square metres does 1kg of putty cover?
Average coverage is about 1–1.2m² per kg for a 2-coat system 1–1.5mm thick, meaning a 40kg bag skims roughly 40–48m². The flatter the render, the better the yield. Exact figures for each BuMaSKIM grade are in the TDS on the website — add 5–10% wastage when estimating for a real project.
How long after rendering can walls be skimmed and painted?
Rendered walls need at least 7 days — ideally 12–14 days in dry conditions — to dry out and let alkalinity stabilise before skimming; after skimming, allow full drying (1–2 days) before applying alkali-resistant primer and topcoats. Skimming or painting damp walls is the leading cause of later blistering, discolouration and paint peeling.
Can exterior putty provide waterproofing?
Yes — FinishSKIM is a finishing putty with built-in water resistance for exterior walls: it smooths the surface while adding a rain-shedding layer beneath the paint film. However, walls under heavy driving rain or with existing damp still need a dedicated waterproofing system (K11 W, WALLCOAT) — waterproof putty reinforces the system, it does not replace it.
What is decorative effect render and where is it used?
Decorative effect render such as Creto is a finishing layer that creates natural textures (concrete, stone or artistic mottled effects) while also providing water resistance, replacing conventional flat paint. It is popular for cafés, showrooms, facades and industrial-style spaces — delivering a distinctive look with genuine weather durability.
What is a lotus-effect protective surface coating?
It is a transparent acrylic, silicone or siloxane topcoat (BuMaSEAL, BuMaSEAL S, S PLUS) applied over walls, tiles or natural stone: rainwater beads up and rolls off like on a lotus leaf, carrying dirt with it. The coating waterproofs the surface, inhibits moss and mould, preserves the building's colour and cuts routine cleaning and maintenance costs.
